Hogwarts: A Mystery
by radiohippie
Summary: John Watson finds himself in the middle of an adventure when helping Sherlock Holmes investigate a series of crimes plaguing Hogwarts castle.  But is there something more sinister behind this rash of petty crimes?
1. Chapter One: First Impressions

**Author's Note: Hello! This is a crossover of Sherlock Holmes and Harry Potter. While I do love to read the Holmes stories, this version is actually inspired by the brilliant BBC series, "Sherlock." This story takes place a year before Harry Potter comes to Hogwarts, so expect to see the same professors and a few familiar, if younger, faces. Cheers!**

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><p>Hogwarts: A Mystery<p>

Chapter One: First Impressions

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><p>"Wait up!" I gripped my broom tightly as I ran up the lawn toward the castle. A throng of gold and burgundy surged ahead of me, holding aloft the man of the hour – Arthur Digby.<p>

"DIGBY! "DIGBY!" The students chanted enthusiastically as they passed through the great wooden doors into the hall. The blonde seventh-year waved his hands in triumph.

As I passed into the entryway, a low voice behind me stopped me in my tracks. "What's all this, then?" I turned to see a lanky, dark-haired boy sitting on the floor, leaning against the wall. He had a large old book in his lap and was surrounded by vials of various liquids. _Odd place to be doing potions homework, _I thought. The boy, who appeared to be a sixth or seventh year student, wore no cloak or sweater – just his white uniform shirt, sleeves rolled to his elbows, and his blue and bronze tie hung loosely around his neck. He raised an eyebrow and looked expectantly at me.

"How could you not know?" I was dumbfounded. "Arthur Digby's just won Gryffindor the first quidditch match of the year!" I was giddy with excitement – the first game of the year always gave me a rush.

The boy looked past me to the crowd celebrating in the entryway. He studied Digby a moment and turned to me. "Too bad he cheated."

My mouth hung wide in shock and the crowd of revelers grew silent behind me as the boy resumed reading the giant tome perched on his knees. Students started whispering as Arthur Digby pushed his way toward the boy, who had once again turned his attention to his book.

"What did you say?" Digby was slightly shorter than average height, though of muscular build. He was known throughout the school for being incredibly sure of himself, which I suppose is a nice way of saying he was a bit of an ass. But three straight years of winning Gryffindor the Hogwarts Quidditch Cup gained him certain allowances.

"I said you cheated, Digby." The Ravenclaw looked up, stone faced, at Digby, whose ears were quickly becoming a bright shade of pink.

I decided to interject, on behalf of Digby and the rest of the team. "But if you weren't there, how could you possibly know something like that?"

The dark-haired lad smirked at me, pointing to Digby's arm. "A twitch. Right there, do you see it?" I looked at Digby and, sure enough, noticed a spasm, slight and intermittent, in the seeker's left hand.

"Surprised you could catch the snitch with that arm, Digby."

Digby crossed his arms to hide his malady. "A nervous habit. I'm right-handed anyway," he quickly added. Arthur's face was growing red and the twitch seemed to be getting worse.

"You've thrown enough balls of parchment at me in Charms for me to know that's a lie. Besides, judging by the rate of acceleration, I'd say the twitch is a recent development. Say, the last five minutes or so." The boy closed his book. "It's getting worse, Digby. I'd get that looked at if I were you."

A pair of red-headed second-years had been standing nearby. "That's all well and good," said one. "But what's a twitch got to do with him cheating?" finished the other.

The Ravenclaw finally stood, towering over Digby, looking down his long nose at the boy. "Oxygenum Liquium. More commonly known in the quidditch world as 'Liquid Agility.'" He paused for a moment, looking expectantly at the group of students. Finally he gave an exasperated sigh. "It oxygenates the blood, increasing the rate of aerobic respiration in the muscle tissue."

The crowd stared at him blankly. "It means you don't get tired! Really, don't any of you read books?"

Digby stepped toward the boy, jamming his finger in his chest. "That's a damn lie. You don't have any proof."

The tall Ravenclaw smirked again. "On the contrary, we have a physical symptom of a potion poorly made." He gestured to Digby's arm. "I'm guessing you ran out of powdered snakeskin, a common problem." The boy began to pace, rubbing his hands together as he did so. "And common problems, as we all know, call for common solutions. In this case, wolfsbane. _Everyone_ knows that these two ingredients have the same basic properties. Except they _don't._ Unlike powdered snakeskin, wolfsbane must be diluted with extract of monksroot when combined with gilly water – the main ingredient in any good agility potion. Because, as every first-year potions student knows, wolfsbane and gilly water can have potentially _lethal_ effects when ingested simultaneously."

The boy stopped in front of Digby and crossed his arms. "I'm going to guess you have about thirty-five minutes until you're seizing on the floor, after which I'm fairly certain your heart will explode in your chest." The color instantly drained from the young Gryffindor's face after hearing the boy's matter-of-fact diagnosis. "I'd get yourself to Madam Pomfrey at once. If this is how you make potions, I'd hate to see you perform a cardionixus charm on yourself – your brain might shut down."

At that moment, Professor McGonagall emerged from the crowd, pushing a few horrified first-years aside to get to Digby, who, by this time, was as white as a sheet. "Mr. Digby," she said when she finally made her way to the boy, "I am appalled at your actions. Putting your own life at risk for the sake of a quidditch match? Never have I seen any of my students behave so foolishly." She turned. "Mister Weasley, kindly escort mister Digby to Madam Pomfrey. After which, mister Digby, you will report to Mr. Filch." Arthur flinched, either at Filch's name or due to the increasing severity of his potion's side-effects, I couldn't tell.

McGonagall addressed the crowd. "In light of this news Gryffindor is hereby disqualified from the game. Tournament points will be awarded to Hufflepuff. Needless to say, fifteen points will be deducted from Gryffindor for poor sportsmanship." She then turned to the young Ravenclaw who, during all the excitement, had sat back down and continued reading his book as if nothing had happened. "As for you, mister Holmes, for exhibiting all of the qualities befitting a Ravenclaw I am awarding ten points to your house."

With that, Professor McGonagall turned to follow Digby, who was now being escorted up the grand staircase by the two young red-headed twins. As the crowd dispersed, angry glares were cast at the young Ravenclaw, who in his studying took no notice.

I stood there a moment, feeling a mixture of crushing defeat and… and odd sense of wonderment. I turned to the boy. "That was brilliant. All that from a twitching hand?"

He spoke, not looking up from his book. "It was _basic_ potions. Arthur Digby is a pompous imbecile who wouldn't know a goblin from a grindylow." He snapped the book closed and began packing his potions into his bag.

"Holmes, is it?" I stuck out my hand. "Nice to meet you, I'm-"

"John Watson." He stood, looking at my hand, but not taking it. "Fifth-year Griffyndor student, beater for the quidditch team, rubbish at potions, but exceedingly skilled in charms."

I stared at the boy. Surely we hadn't met before. And, if we had, I felt terrible that his name had slipped my memory.

Holmes slung his bag over his shoulder. "If you'll excuse me, Watson, I have some work to do in the library. Perhaps we'll see each other again sometime."

With that, he started off toward the staircase, leaving me to stand dumbfounded in the entrance.

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><p>"O-Levels are coming up this year, John. All I'm saying is that it might be beneficial to ask for a little extra help."<p>

It was two o'clock and Sarah Sawyer, Oliver Wood, and I sat at one of the tables in the Great Hall. Oliver, while pretending to study for our upcoming arithmancy exam, was too busy drawing up quidditch plays to pay attention to our conversation.

"I'm fine on my own." I absently turned the pages in my book as Sarah glared at me from across the table. "Besides, what would I do with potions, anyway? I'm a lost cause, Sarah."

Refusing to leave it at that, Sarah shoved a piece of parchment at me across the table. "Just look at it, John."

_Ravenclaw Mentorship Program Application_

I sighed. "I don't need a mentor, Sarah."

Oliver looked up from his doodles. "I'd listen to her, John. You'll never hear the end of it."

I reluctantly picked up the paper. Attached was a list of the available mentors – all Ravenclaws, obviously. As I scanned the list, one name stood out.

_Sherlock Holmes._


	2. Chapter Two: Hogwarts Detective Agency

Hogwarts: A Mystery

Chapter Two: The Hogwarts Detective Agency

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><p>"I can't believe this." Oliver followed me down to the Gryffindor common room from the dormitory, slipping his sweater over his head as we came down the stairs. "You're really going to be studying with that pompous ass?"<p>

"Oliver, you're just sore that Holmes lost us the first game of the year." We joined Sarah, who was already sitting at one of the tables near the wall.

She looked up from her books. "Not to mention twenty points from Griffyndor, John." She angrily scratched her quill across her parchment. "I can't believe you."

"You're the one who told me to sign up, Sarah." Oliver and I sat at the table, puling out our arithmancy books. "Besides, you saw what he did to Digby. Holmes can tell a botched potion from a twitching arm – it's incredible!"

Sarah rolled her eyes. "Like you've said."

"A thousand times," Oliver added. "We get it, he's some kind of potions genius."

"Oh for goodness' sake, Oliver!" I looked up from my book to see Sarah grab one of Oliver's parchments from across the table. "If you spent half the time studying Arithmancy as you did on drawing up quidditch doodles, you'd be better than Professor Vector by now!"

Oliver snatched the parchment from Sarah's hand. "They're plays! I'm going to be team captain next year," he squinted his eyes. "Even if it kills me."

"It probably will," I added, unrolling my parchment in front of me. No sooner than it was open the paper began to emit a dull green light. Scrawling words were forming on the page.

_Meet me in the library at one o'clock, if convenient. – SH_

Sarah and Oliver gawked at my paper in amazement. "That's enchanted ink!" Sarah grabbed the parchment and held it up.

"That's actually pretty impressive, John." Oliver grinned, leaning over to look at the paper as the glow appeared again. Sarah set in on the table, revealing another message.

_If inconvenient, come anyway. – SH_

Oliver shook his head. "What did I tell you – an arrogant knob."

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><p>Sherlock Holmes set a large stack of books on the table in front of me with a thud. "Alright, Watson," he sat down across from me. "I'm going to tell you something that most students don't seem to understand." He pulled out his wand, which was bent and well-worn from use. "You don't need one of these to do magic." He set the wand on the table. "Potions isn't chemistry, John – it's a magical art. It takes just as much skill and thought as casting a spell or divining the future."<p>

Holmes rustled around in his bag for a moment, pulling out a few vials and placing them on the table.

I pulled away. "Is that-"

"Goblin knuckles. Very rare and highly useful." He didn't look up from what he was doing.

"Um, you walk around with a jar full of knuckles in your bag?"

He looked up at me, his face very serious. "Where else would you suggest I keep them?" He didn't wait for a response, instead gesturing to the items on the table. "Each of these ingredients has a magical property – a spell of its own inside. When combined they can perform any kind of magic you want them to. But in order to understand the potion, you have to understand what each of its ingredients." He turned one vial over in his hand absent-mindedly. "It's a bit like baking a cake, really. I can't imagine how anyone goes about making anything if they don't know what they're using. But, alas, they do."

Holmes leaned back in his chair, rolling his sleeves to his elbows. I looked down at the books he had placed in front of me. _Magical Plants and Herbs; 1001 Uses for Monksroot; Serums, Elixers and Other Potions_. I picked up one of the larger ones. "_A History of Chemical Alchemy_? We were never assigned this in class."

Holmes shook his head. "Of course we weren't," he said, folding his arms across his chest. "Professor Snape is one of the most intelligent professors in the school. His ability to actually impart his knowledge to the students, however, is somewhat lacking. I assume it's because he hates them, " he added with a shrug.

At that moment Holmes and I both turned at the sound of approaching footsteps. "_Holmes!_" The voice belonged to a dark-haired boy quickly striding toward us through the library, his cloak billowing behind him. On his chest was they yellow badge of Hufflepuff. "I need to talk to you."

I turned to Holmes, who rolled his eyes at the boy, who was now standing at the end of our table. He gestured to our visitor. "John Watson, this is-"

"Gregory Lestrade," I said, recognizing the boy immediately. "Head boy of Hufflepuff, right?"

I held out my hand and Lestrade shook it firmly. "And you're the beater for Gryffindor. Shame about Digby," he added with a smirk. He turned back to Holmes. "Did you get my note?"

Sherlock pulled out a small piece of parchment from his pocket and held it aloft. "Oh, you mean this? Yes, along with the other eight notes you've sent me this week." He held his wand to the note, which promptly burst into a million tiny blue stars. "The answer is still no, I'm afraid."

Lestrade groaned in frustration, leaning on the edge of the table. "Holmes, please. We need your help. You'd be perfect for it."

"I know I would be," Holmes said, opening one of the many volumes on the table and skimming its pages. "And I'd consider it if I thought you and your friends could achieve your objectives with any sort of competency."

I looked from one boy to the other. Holmes was attempting to ignore him, but Lestrade seemed desperate. "What… what are you two on about?"

"The Hogwarts Detective Agency," Lestrade said, turning to me.

"It's idiocy."

"It's necessity." Lestrade shot Holmes an angry glare. "There's been a rash of crimes in the castle and no one's bothered to investigate." He turned to Sherlock. "We're not talking chocolate frogs here, Holmes. Someone's stealing _wands_."

Holmes looked up from his book. "Wands?"

I turned to Lestrade. "How could someone get into the dormitories?"

"That's just it – they can't. The locations of the dormitories are known only to the members of each house, as are the passwords." He stood upright, pulling back his cloak to rest his hands on his hips. "We might be looking at a group of students."

"A group?" Sherlock was giving Lestrade his full attention now, hands clasped in thought.

"Well, the wands were taken from different houses."

"All the houses?"

"All of them. As far as I know none of the professors are looking into it."

"That's odd," I said. "Now that you mention it, there have been a few more first-years looking for their wands than usual lately." I shrugged. "I always figure they've lost them."

Lestrade shook his head, "I don't think so. But none of the professors are listening to me."

We sat silently for a moment. I looked at Sherlock, who had picked up his wand and was now gnawing at the tip in thought. _So that's why it looks like that_, I thought. Finally he took it from his mouth.

"Fine."

Lestrade raised an eyebrow. "Really?"

"Yes, but I'm not joining your little club. I refuse to work with Anderson, he is insufferable." He closed his book and began packing his vials into his bag. "Watson, pack up your things, we're going down to the Hall."

I tilted my head. "Wait, you want me to go with you?"

"Of course," he said, vials clinking as he packed them away. "I need an assistant." He looked up at me. "That is, if you don't mind."

I only had to think for a moment. "Not at all."

"Good." He slung his bag over his shoulder. "Then let's waste no more time." He turned to Hufflepuff, who stance was proudly triumphant. "Thank you, Lestrade, I shall take it from here."

The boy's face dropped. "What? No. I'm coming, too, Holmes, this is _my_ case!"

Sherlock shook his head at Lestrade. "Case? Really? I think you're taking yourself a little too seriously."

"Look who's talking."

Sherlock pulled at my arm, guiding me ahead of him. "Alright, let's go."

With that, the three of us headed out of the library toward the Great Hall.


	3. Chapter Three: Preliminary Investigation

Hogwarts: A Mystery

Chapter Three:

"Katie, did you hear anyone enter your dormitory last night?"

The young Gryffindor shook her head, her braids shaking side-to-side. "No. I thought I lost it. My mum is going to be so mad at me."

Sherlock was crouching before the tiny first year, stone-faced and scribbling notes in a tiny book. "Most likely. Wands are fairly expensive."

"Hey!" I sat down next to Katie, resting my hand on her shoulder. "It'll be okay."

"I have a big Charms exam coming up and I don't know how I'll get through it without a wand." She rubbed the heel of her shoe against her ankle nervously and looked at me.

"I'm sure Professor Flitwick will understand." I looked at Sherlock, who tucked his notebook into his back pocket and stood.

"Well, Miss Bell, thank you for your time. It's possible that even you weren't absent-minded enough to lose a witch's most important possession. There may be a wand-thief on the loose in this castle and I intend to apprehend him." He scanned the rest of the Great Hall as if the culprit would present himself to us.

Lestrade, who had been watching Holmes' interrogation silently finally spoke up. "That's the sixth student we've talked to this morning. And all have lost their wands in the last week. That's a pretty high rate, don't you think?"

"Unusually high," Holmes replied, taking his own wand from his pocket. "And no one heard or saw anything." He flicked his wrist, levitating a spoon from the table and watching it slowly twirl on an invisible axis. "So far, all of the victims have been first-years."

"If anyone wanted to steal a wand, first-years would be the best target," I added, hoping to contribute something useful to the investigation.

"Obviously," said Holmes curtly. "Dozens of wands are lost every year at Hogwarts, most of them misplaced by first-years." He flicked his wand again and a fork now joined in a dance with the spoon. "Like Lestrade said, none of the professors think it's anything to be worried about – it's simply students misplacing their wands."

"Only it's not," Lestrade interjected. "Someone is taking them."

"But what would you want with someone else's wand? The wand chooses the wizard, right?" I was beginning to doubt whether this really was a case of robbery, or if this year's new students were just unusually absent-minded.

"We have to investigate the scenes of the crimes." Sherlock flicked his wand again, sending the cutlery clattering to the table. He abruptly turned on his heel and headed to the doors of the Hall.

"But Sherlock, we can't come with you." Lestrade and I quickly followed the lanky Ravenclaw out of the Hall. "We're all from separate houses."

"Good." Sherlock's brisk pace didn't falter. "I'll finally be allowed to think."

"Lestrade!" Just before we reached the end of the Hall, a voice called to us from the direction of the Ravenclaw table. A thin dark-haired boy approached us followed by a short dark girl from Hufflepuff.

"Lestrade, we've been looking for you everywhere," the girl said. I recognized her as Sally Donovan, a fourth-year. The boy whom she followed was called Anderson – a Ravenclaw. His first name had slipped my mind. Donovan continued. "Anderson's wand's been stolen."

Sherlock stopped in his tracks, wheeling about to face the two of them, yet saying nothing.

"Are you sure?" Lestrade looked at the boy gravely.

"You've not left it in the bathroom again, have you, Anderson?" Sherlock sneered at his fellow Ravenclaw. "I'd hate to see Peeves get a hold of it again."

Anderson shot a glare at Sherlock. "No, Holmes, I'm certain I had it when I went to bed last night. I used it to reduce the blister on the bottom of my foot." Donovan looked at him in disgust. "What? It was really giving me trouble."

Without asking, Sherlock grabbed the bag from Anderson's shoulder.

"Hey!"

Sherlock opened the bag and peered inside. "You've used an extension charm on this, haven't you, Anderson?"

The boy nodded. "Y-yes. Give me back my bag, Holmes."

After rummaging around in Anderson's bag for a moment, Sherlock drew his wand from his pocket. "_Accio wand._" Immediately several items burst forth from Anderson's bag – a few chocolate frogs, some tiny dinosaur figurines and, finally, his wand, which hit the floor with a loud clatter.

Anderson's face turned beet red as he quickly snatched up his wand, jamming it into the pocket of his cloak.

Lestrade looked at the floor. "What's with the dinosaurs?"

"I'm researching their anatomic relation to various species of modern dragon," the boy said, swiping the tiny reptiles off the floor.

Sherlock glared down at him. "Next time, Anderson, save us all the trouble and cast a summoning charm before you go sounding the alarm. You lower the IQ of the whole Hall."

"Ease up, Sherlock." I attempted to come to Anderson's rescue, as he packed the last of his things in his bag, handing me a chocolate frog as he did so.

"Where are you all heading?" He asked.

"We're investigating the robberies," Lestrade replied. "We've interviewed some of the students, but now we have to investigate the crime scenes."

Anderson grinned. "Well, we've already done that!"

Sherlock raised an eyebrow at him. "Really? And what did you find?"

The grin faded. "Well, nothing, actually."

"I'm beginning to doubt whether it's really theft at all," Donovan stated, mirroring my earlier opinion.

Sherlock shook his head and started out of the Hall once more. "Really, Anderson, the fact that you are a Ravenclaw never ceases to make me doubt my faith in the Sorting Hat."

"What?"

"What have you _observed?_ What did you see?" We reached the center of the entryway and Sherlock stopped once again, addressing all of us. "I have to ask you all to stop following me. Everyone go back to your own common rooms, investigate on your own. _Be thorough_. We'll all meet in the library once we've gathered as much data as possible."

"What about Sally and I?"

"Sally, you can come with me." Lestrade took her by the arm. "We'll see you all later."

Sherlock, Anderson and I stood in the entryway for a moment. Anderson turned to Sherlock expectantly. "Well, I guess this means it's-"

"You are not following me." Sherlock and I both headed for the staircase, leaving Anderson to stand alone in the entryway.

"That may have been a bit rude," I whispered once we had gotten out of ear-shot.

"It was true, so I said it."

"Well, in your case, honesty might not always be the best policy."

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><p>The first year dormitory was smaller than I had remembered it four years ago. <em>Four years<em>. It seemed like forever ago that I thought magic was only something that happened in fairy-tales. Before a strange visitor showed up at my door with some surprising news for my parents and I.

I looked around the room, but nothing jumped out at me right away. It was a typical first-year's room – robes strewn about the floor, liquorice wand wrappers scattered here and there. A giant copy of _Hogwarts: A History_ sat open on one of the beds revealing a picture of a young Albus Dumbledore, smiling and waving from the pages of the book.

"This is it." Young Cormac McLaggen led me to his trunk, which had clearly been given a thorough rummaging through.

"I see you've already been through it." I looked down at the trunk, feeling a bit discouraged. If there had been any evidence here, it may well be gone by now.

"I can't find it anywhere, it must have been stolen." The young boy gritted his teeth. "I didn't lose it! I never lose anything."

"Well, would you mind if I have a poke around?" I asked, already scanning the room for any clue of the perpetrator.

"Not at all." He shook his blonde head. "I'll bet you it was that Lee Jordan. Always running around with those Weasley boys pulling pranks on the first-years." He crossed his arms and sat on the edge of his bed. I tried not to let his pouting distract me from my purpose.

I scoured the area around McLaggen's trunk for any signs of trespassing. The boy had obviously been rifling through it, tossing items aside in search of his missing wand. However, somehow something caught my eye amidst the pile of clothes and books. A glint of light from just under the bed. I reached out and took in my hand a small blue stone, polished and seeming to glow with a light from within.

"What's this?" I handed the stone to McLaggen who inspected it for a moment.

He shrugged. "No idea. It might be Rupert's – he's always leaving his stuff about." He dropped the stone into his pocket. "I'll be sure to give it to him later."

I resumed my search of the room. The windows were all secure and there seemed to be no signs of anyone breaking in. Perhaps it really had been one of the other first-years.

"Did you hear anything last night, McLaggen?"

He shook his head. "No, but I'm a pretty hard sleeper. I've missed a few classes this year because of it."

I sighed, scanning the room a final time. I didn't know what Sherlock had expected me to find, but I felt there was little else I could do. "Well, thanks."

I crossed the room to the door feeling as though my search had been in vain. I had found no evidence that could lead us to the wand thief. Hopefully Holmes and the others had had better luck than I.


End file.
